1. Field of the Invention
The present invention relates to a method for establishing a packet data communication connection in a communication network between a first user equipment and a second user equipment and also to a corresponding device. In particular, the present invention is directed to a method and a corresponding device in a packet data communication system.
2. Discussion of the Related Art
Recently, the usage of mobile telecommunication systems for transmitting and receiving data besides speech gains increasing importance. A method for performing such a data communication is to form data packets which are transmitted via the communication network. This packet data is used for example in the GPRS system (General Packet Radio Service) in GSM or in a packet data communication in a 3rd generation UMTS (Universal Mobile Telecommunication System).
Subscribers can use said packet data communication, e.g., for visiting the World Wide Web (WWW) or the like. Therefore, it is possible to communicate with a large number of different nodes in the Internet. Furthermore, data exchange between mobile stations or user equipments is also possible by using a packet data communication.
In the case of the above mentioned GPRS systems, a data communication between user equipments such as mobile stations or other terminals requires several additional network elements and procedures. In FIG. 5 a simplified example of such a communication system is shown.
Components of said network besides the respective user equipment UE 1, UE 2 of subscribers are, e.g., base station subsystems (BSS) as a transceiver part for a communication between the network and the user equipment, serving GPRS support nodes (SGSN) controlling at least one respective base station subsystem (i.e., serving a respective subscriber roaming in the corresponding network area) and performing security functions and access control. The serving nodes are further connected to gateway GPRS support nodes (GGSN) which provide interworking with external packet switched networks. Additionally, at least one database such as a home location register (HLR) is provided which includes subscriber specific information used by the corresponding network elements for the communication.
Data packets are tunneled between said serving node and said gateway node by using a GPRS tunneling protocol (GTP) tunnel which is defined by associated packet data protocol (PDP) contexts. Said PDP contexts are information sets including identification information, address information and the like.
A packet data communication is performed by using different path protocols like internet protocol (IP) or some other packet data protocols.
According to the prior art, when a packet data communication for example between two mobile stations is to be performed by using a communication system like GPRS, on the calling side, the data is routed from the calling mobile station UE 1 via the serving node SGSN to the gateway node GGSN. The gateway node on the calling side communicates with the gateway node on the terminated side via a packet data network (PDN) such as the public Internet by using a packet data protocol such as IP. Therefore, corresponding addresses, for example the IP address, of each mobile station has to be known to the system. These addresses are provided by the GPRS. On the terminated side, data is routed from the gateway node GGSN 2 via the serving node SGSN 2 to the called mobile station UE 1. Hence, according to FIG. 5, data flows UE 1 ->BSS 1->SGSN 1->GGSN 1->PDN->GGSN 2->SGSN 2->BSS 2->UE 2 and vice versa, respectively.
However, the above described packet data communication is not optimal for a communication between two user equipments served by the system by using for example IP or the like over an extended period of time. Since such a communication, for example for an IP telephony, an IP video-telephony or surveillance applications, is performed via the public packet data network and therefore via the gateway nodes GGSN, the load for network resources is unnecessarily high. Furthermore, the security level of the connection depends on the security level of the used public network. As the load of some public networks, for example of the Internet, varies in a wide range, a transfer rate and Quality of Service (QoS) could decrease extremely in case of increasing load.
Another drawback of the above described communication method is that the IP address (or other packet data protocol addresses) of the corresponding user equipments must be known beforehand. However, these addresses are usually allocated dynamically, i.e., they are changed.
In the article “Concepts, Services, and Protocols of the New GSM Phase 2+ General Packet Radio Service” by Brasche, G., et al, IEEE Communications Magazine, vol. 35, no. 8, pages 94–104, Aug. 1, 1997, a packet data communication network is described in which a gateway support node GGSN is involved in packet data communications between two mobile stations.
Document WO 97/21313A describes a routing procedure in a packet data communication network using a SGSN and a GGSN. A fixed number is used to address the SGSN currently in use.